Stiffness, not inertial coupling, determines path curvature of wrist motions

2012 ◽  
Vol 107 (4) ◽  
pp. 1230-1240 ◽  
Author(s):  
Steven K. Charles ◽  
Neville Hogan
Keyword(s):  
Realistic Model ◽  
Laser Pointer ◽  
Dominant Term ◽  
Ulnar Deviation ◽  
Inertial Coupling ◽  
Planning And Control ◽  
Flexion Extension ◽  
Path Curvature ◽  
And Control ◽  
Wrist Stiffness

When humans rotate their wrist in flexion-extension, radial-ulnar deviation, and combinations, the resulting paths (like the path of a laser pointer on a screen) exhibit a distinctive pattern of curvature. In this report we show that the passive stiffness of the wrist is sufficient to account for this pattern. Simulating the dynamics of wrist rotations using a demonstrably realistic model under a variety of conditions, we show that wrist stiffness can explain all characteristics of the observed pattern of curvature. We also provide evidence against other possible causes. We further demonstrate that the phenomenon is robust against variations in human wrist parameters (inertia, damping, and stiffness) and choice of model inputs. Our findings explain two previously observed phenomena: why faster wrist rotations exhibit more curvature and why path curvature rotates with pronation-supination of the forearm. Our results imply that, as in reaching, path straightness is a goal in the planning and control of wrist rotations. This requires humans to predict and compensate for wrist dynamics, but, unlike reaching, nonlinear inertial coupling (e.g., Coriolis acceleration) is insignificant. The dominant term to be compensated is wrist stiffness.

scholarly journals The passive stiffness of the wrist and forearm

2012 ◽  
Vol 108 (4) ◽  
pp. 1158-1166 ◽  
Author(s):  
Domenico Formica ◽  
Steven K. Charles ◽  
Loredana Zollo ◽  
Eugenio Guglielmelli ◽  
Neville Hogan ◽  
...  
Keyword(s):  
Wrist Joint ◽  
Rehabilitation Robot ◽  
Passive Stiffness ◽  
Ulnar Deviation ◽  
The Past ◽  
Stiffness Matrices ◽  
Flexion Extension ◽  
Stiffness Characteristics ◽  
Wrist Stiffness ◽  
Rotation Dynamics

Because wrist rotation dynamics are dominated by stiffness (Charles SK, Hogan N. J Biomech 44: 614–621, 2011), understanding how humans plan and execute coordinated wrist rotations requires knowledge of the stiffness characteristics of the wrist joint. In the past, the passive stiffness of the wrist joint has been measured in 1 degree of freedom (DOF). Although these 1-DOF measurements inform us of the dynamics the neuromuscular system must overcome to rotate the wrist in pure flexion-extension (FE) or pure radial-ulnar deviation (RUD), the wrist rarely rotates in pure FE or RUD. Instead, understanding natural wrist rotations requires knowledge of wrist stiffness in combinations of FE and RUD. The purpose of this report is to present measurements of passive wrist stiffness throughout the space spanned by FE and RUD. Using a rehabilitation robot designed for the wrist and forearm, we measured the passive stiffness of the wrist joint in 10 subjects in FE, RUD, and combinations. For comparison, we measured the passive stiffness of the forearm (in pronation-supination), as well. Our measurements in pure FE and RUD agreed well with previous 1-DOF measurements. We have linearized the 2-DOF stiffness measurements and present them in the form of stiffness ellipses and as stiffness matrices useful for modeling wrist rotation dynamics. We found that passive wrist stiffness was anisotropic, with greater stiffness in RUD than in FE. We also found that passive wrist stiffness did not align with the anatomical axes of the wrist; the major and minor axes of the stiffness ellipse were rotated with respect to the FE and RUD axes by ∼20°. The direction of least stiffness was between ulnar flexion and radial extension, a direction used in many natural movements (known as the “dart-thrower's motion”), suggesting that the nervous system may take advantage of the direction of least stiffness for common wrist rotations.

On the Dynamics and Control of a Full Wrist Exoskeleton for Tremor Alleviation

2019 ◽  
Author(s):  
Jiamin Wang ◽  
Oumar Barry ◽  
Andrew J. Kurdila ◽  
Sujith Vijayan
Keyword(s):  
Controller Design ◽  
Human Motion ◽  
Structural Function ◽  
Wrist Flexion ◽  
Unknown Parameters ◽  
Ulnar Deviation ◽  
Marquardt Algorithm ◽  
Flexion Extension ◽  
Dynamics And Control ◽  
And Control

Abstract This paper introduces a novel wearable full wrist exoskeleton designed for the alleviation of tremor in patients suffering from Parkinson’s Disease and Essential Tremor. The design introduces a structure to provide full observation of wrist kinematics as well as actuation in wrist flexion/extension and radial/ulnar deviation. To examine the feasibility of the design, the coupled dynamics of the device and the forearm is modeled via a general multibody framework. The dynamic analysis considers human motion, wrist stiffness, and tremor dynamics. The analysis of the model reveals that the identification of the wrist kinematics is indispensable for the controller design. Nonlinear regression based on the Levenberg-Marquardt algorithm has been applied to estimate the unknown parameters in a kinematic structural function designed to approximate the wrist kinematics, which leads to the construction of the control system framework. Finally, several simulation cases are demonstrated to conclude the study.

PLANNING TO MEET THE GROWING DEMANDS ON NORTHLANDS WATER RESOURCES

1986 ◽  
pp. 33-42
Author(s):  
D.L. Roke
Keyword(s):  
Industrial Development ◽  
Water Resource Management ◽  
Limited Resources ◽  
Careful Planning ◽  
Management Planning ◽  
Planning And Control ◽  
Sources Of Pollution ◽  
And Control ◽  
Resource Management Planning ◽  
Pastoral Farming

The growth in horticultural and some industrial development in selected areas of Northland has led to a need for more specific and careful planning and control of limited resources in a number of major catchments. The potential irrigation demands for horhculture comprise over 60% of Northland's potential water requirements. By contrast, farm water supply needs are only 11% of these needs. Because of their importance to the Northland economy, and in the legislation these needs are given a high priority in water resource management planning. Land uses, including pastoral farming, require careful operation to reduce diffuse sources of pollution.

Problems of Optimization in the Planning and Control of the Environment

Soviet Review ◽  
1973 ◽  
Vol 14 (2) ◽  
pp. 24-38 ◽  
Author(s):  
N. Fedorenko ◽  
K. Gofman
Keyword(s):  
Planning And Control ◽  
And Control
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